Starmail is an in-game mechanic found through the Ranch House menu by clicking the "Starmail" button. It allows the player to read any Starmail the player receives over the course of the game. Any unread Starmail is automatically considered read once opening it.
Since Starmail is the trigger for some of the major features unlocked during the course of the game, reading Starmail is required to fully progress in the game.
Starmail is received when certain requirements have been met. If a certain starmail is in a series of starmails, such as Rancher introduction Starmails, it must be read before being able receive the next one. Certain Starmail act as triggers to unlock new features, such as the 7Zee Rewards Club, so must be opened to be able to receive them.
While Starmail does not allow the player to directly respond to received starmail, some of Casey's responses appear to be to a previous conversation, which implies that Beatrix responds to them when reading them.
1.0.1 - Starmail popups now disappear once you’ve read the mail.
1.0.0 - Added the final Hobson journal nodes and Casey starmail to Adventure Mode. Reading both is required for ‘completing’ Adventure Mode.
0.6.0 - Starmails from Casey have been overhauled to reduce feelings of clinginess, be less dramatic, and fit more with the tone of the game. However, the conclusion to the story remains unchanged.
0.5.1 - The 7Zee Rewards Club is a new feature that rewards highly successful ranchers with unique rewards. Starting at noon on day 7 you’ll receive a starmail form 7Zee introducing you to the rewards club. You must read the starmail in order to unlock the rewards club.
You will now receive occasional starmails from Casey, someone important to Beatrix whom she left behind back on Earth. Both Casey and Hobson’s story will be completed in a future update.
Starmail now has an unread mail notification showing you how many unread mails you still need to read. Hopefully it doesn’t cause as much anxiety as the one you stare at in real life, reminding you that you should be replying to those emails instead of reading Slime Rancher patch notes.
The starmail interface has received some visual improvements and readability changes.
0.4.0 - Starmails that notified you of new items in the shop have been removed and replaced with pedia-style pop up notifications. Starmail will now be reserved for only the most important missives, and perhaps an occasional request for newbucks from a galactic prince.
Fixed confusing no-longer relevant bit in starmail from Thora.
0.3.0 - Entering the ranch house still pauses time, but Starmail cannot be accessed in 5-Day Rush.
0.3.0b - Fix missing StarMails.
0.2.5 - Fix bug where the Starmail content did not initially scroll to the correct position.
0.2.2 - Fixed bug where starmail was lost on game reload.